The goal of the proposed research is to understand how receptors for neurotransmitters function, and how the cell controls the functional properties of its receptors. Acetylcholine receptors on mammalian cells will be studied by biophysical methods to determine their functional properties. Previous work has provided a quantitative picture of normal receptor function in clonal mammalian muscle cells, and has shown that receptor function can be modified by treatments which alter carbohydrate processing on glycoproteins and by a component in serum. The proposed work will determine the nature of these functional changes and will examine the cellular mechanisms by which the changes are produced. Further studies will determine the effects of receptor phosphorylation and membrane lipid composition on receptor function in these clonal muscle cells. The performance and interpretation of these studies utilize the information available on the function, structure and metabolism of acetylcholine receptors in these cells, and take advantage of the experimental manipulability of clonal cells. The information provided will give insight into the mechanisms the cell uses to control receptor function. Additional experiments will examine the function of acetylcholine receptors on muscle fibers from developing mice. The data will be analyzed to determine the number of functionally distinct classes of acetylcholine receptors expressed by muscle fibers, and will be related to data obtained from clonal cells. Finally, studies of nicotinic acetylcholine receptors on clonal mammalian neural cells will be initiated. The results of these studies will be compared and contrasted to those from muscle nicotinic receptors, to provide insights into the function of neural nicotinic receptors and into similarities and differences in cellular control of receptor function in the two cell types. The results of these studies are required to form a quantitative picture of the function of acetylcholine receptors, and to determine how the cell controls the function of receptors. Such a picture is necessary to understand cholinergic synaptic transmission and the mode of action of pharmacological agents. Further, it is required to evaluate changes in synaptic function during development or after pathological processes. In more general terms, the insights gained are applicable to the overall question of the control of the ionic permeability of biological membranes.